In recent years the renewable lignocellulosic materials, herein also designated as “lignocellulosics”, such as straw, wood, paper wastes, were attracting increasing attention due to the limitation of raw oil sources on earth.
The idea of using of ligninocellulosics as a potential raw source for fuels and synthetic polymers production is not new. In general, there are two main pathways for the conversion of lignocellulose into valuable intermediates:    1) The “Thermochemical platform”, wherein the lignocellulose is converted to low molecular products, such as EtOH, phenolics etc, which may be further converted to desired products; and    2) The “Sugar platform”, wherein the polymeric structure of the hemicellulose, cellulose and lignin are of main interest and the desired products are polymers and are built upon the natural polymeric structures.
The present invention follows the second pathway. For that the natural polymeric components lignin, hemicellulose and cellulose are to be separated from each other as pure as possible since the contamination of the sugars in the lignin and vice versa leads to a significant worsening of the isolated material. The lignocellulosic component separation in good purity is very challenging mostly due to the presence of mixed fractions, so-called lignin carbohydrate complexes (LCC), which is a complex mixture of the covalently bound polymeric sugars and lignin.
The classical delignification processes operate with unselective pulping methods, wherein the lignin is removed simultaneously with hemicellulose and LCC at high temperatures, very often in the presence of sulfur containing reagents. The structure of the removed lignin is drastically changed during such treatment that affects its further application in the polymer chemistry. Moreover, the simultaneous removal of lignin, LCC and hemicellulose makes it practically impossible to separate sugars from the lignin to pursue “lignin-in-pure-form-separation”. To achieve the high lignin purity the polymeric sugars in the lignin liquor have to be cleaved to their monomers. This makes the use of the natural hemicellulose polymeric structure impossible. In another aspect the LCC might remain in the hemicellulose stream after lignin separation, thus contaminating the hemicellulose products.
A great technical improvement in this area could be the development of a method, by which sugar free lignin is gently separated from the lignocellulosic material, whereby cellulosic material enriched with LCC and hemicellulose is obtained, followed by LCC separation from said material providing the cellulosic material enriched with hemicellulose. That is one task of the present invention.